Electron tube and cathode therefor



y 17, 1966 J. A. JOLLY 3,252,040

ELECTRON TUBE AND CATHODE THEREFOR Filed June 19, 1963 2 Sheets-Sheet l INVENTOR. JAMES A. JOLLY ATTORNEY May '17, 1966 .1. A. JOLLY ELECTRON TUBE AND CATHODE THEREFOR 2 Sheets-Sheet 2 Filed June 19, 1963 INVENTOR. JAMES A. JOLLY ATTORNEY United States Patent 3,252,040 ELECTRON TUBE AND CATHODE THEREFOR James A. Jolly, San Carlos, Calif., assignor, by mesne assignments, to Varian Associates, a corporation of California Filed June 19, 1963, Ser. No. 288,994 7 Claims. (Cl. 313-256) This invention relates generally to electron tubes and more particularly to a quick heating cathode for use in an electron tube.

Push to talk transmitters and other similar devices require tubes having quick warm up operation and low heater power consumption. In this type of electronic equipment, and also in other electrical systems utilizing tube components in cooperation with solid state components, it is essential for the tube to have a rapid warm up time and low heater power consumption.

Directly heated cathodes generally consume less power, and have a shorter warm up time and indirectly heated cathodes. However, the RF. energy to be amplified is faced with a long inductive path in the directly heated cathodes of the prior art.

Indirectly heated cathodes of the prior art provided, generally, a short inductive path for the RF. energy being amplified and furthermore, the entire indirectly heated cathode is at one potential thereby making the electron flow from the cathode more eflicient. However, indirectly heated cathodes generally consume a lot of heater power and require substantially long warm up time before electron emission is achieved.

A need existed for a tube having low heater power consumption, quick warm up time, and a short inductive path for the RF. energy that is to be amplified.

Accordingly, the main object of this invention is to provide an electron tube which has low heater power consumption and will heat up to operating temperature in a very short period of time.

A further object of this invention is to provide an electron tube which has a short inductive path for the RF. energy that is to be amplified.

A still further object of this invention is to provide a directly heated cathode having a short inductive path for the RF. energy that is to be amplified.

Another object of this invention is to provide a bypass capacitor in a cathode assembly to shorten the reactive path for the RF. energy that is to be amplified.

A further object of this invention is to provide a relatively thin, sturdy, cathode assembly having low thermal capacity.

Briefly described, the invention resides in a cathode assembly which comprises a metallic mounting member for carrying RF. energy that is to be amplified. An insulating layer is applied to the metallic mounting member. Metal means are provided on the surface of the insulating layer. The metal means are capacitively coupled through the insulating layer to the metallic mounting member to shorten the inductive path for the RF. energy to be amplified, The metal means have an electron emissive portion which forms the surface for emitting electrons from said cathode assembly, and a substantial part of the electron emissive portion is not capacitively coupled to the mounting member.

In addition, an electron tube having an envelope enclosing electrodes including a cathode is described.- The cathode of the electron tube comprises a metallic mounting member, an insulating layer, and metal means capacitively coupled through the insulating layer to the metallic mounting member. The metal means have an electron emissive portion which forms the surface for emitting electrons from said cathode assembly, and a substantial 3,252,646 Patented May 17, 1966 FIGURE 2 is a sectional view on the vertical axis of V the cathode assembly of the tube of FIGURE 1;

FIGURE 3 is a sectional view of the cylindrical ceramic member used in the cathode of FIGURES 1 and 2;

FIGURE 4 is a series arrangement of the metal bars used in the cathode; and

FIGURE is a parallel arrangement of the metal bars used in the cathode.

Referring to FIGURE 1, a tetrode is shown to illustrate the invention. The external anode tetrode structure of FIGURE 1 comprises an envelope having a vitreous section 2 sealed between a flange 3 on tubular anode 4 and a metallic terminal ring 6 located below the anode. A

disk-like vitreous header 7 is sealed to ring 6. By the term vitreous I means a material having insulating and vac-tight properties, such as glass, ceramic or the like.

Ring 6 and anode flange 3 may be of a suitable glasssealing metal, such as Kovar, and cup-shaped anode 4 may be of copper. The tube is preferably exhausted through a metal tubulation 8 on the anode, which tubulation is pinched off at tip 9. Heat is removed from the anode by providing heat removal means (not shown) about the anode 4.

The internal electrodes of the tube comprise a cathode 14, control grid 16 and screen grid 17. These are tubular electrodes projecting into the anode and coaxial therewith. The two grids have upper free ends and lower fixed ends and are preferably madeof wire bars, the screen grid preferably being capped by top piece 18. Screen grid 17 is supported from its lower end by a bracket 19 fastened by screws 20 to a flange 21 secured to envelope ring 6. By this arrangement the ring 6 serves as a terminal for the screen grid.

The remaining electrodes are connected to and supported by rigid contact prongs sealed to header 7. As shown, a plurality of prongs 22, 23, 24 and 26 are arranged in arcuate formation, such as a circle concentric with the header. Another prong 27, preferably of larger diameter than the others, is located inside the arcuate formation, the preferred location being at the center of the header. All these prongs are rigid rods so that they are adapted to be plugged directly into a socket. Being of heavier stock, the center prong gives added support for the tube in the socket.

Control grid 16 is preferably connected to center prong 27 by a supporting bracket 28, which bracket may conveniently be of U-shape brazed at the center to the top of prong 27 and at the ends to opposite sides of grid band 29. By connecting the control grid to center terminal prong 27, which prong is concentric with terminal ring 6, it will be seen that the external terminals of the two grids are coaxially arranged. Such an arrangement is particularly desirable in circuits for higher frequency operation employing coaxial lines.

Referring to FIGURE 2, the cathode 14 comprises a cylindrical mounting member 30 supported by an annular cathode support 31 having four support brackets 32, only two of which are shown in FIGURES 1 and 2. The support brackets 32 shown in FIGURE 1 are connected to prongs 24 and 26, and the remaining support brackets (not shown) are similarly connected to prongs (not shown). The mounting member 30 is formed of a thin metal, such as one mil thick Hastelloy B which is a trade conjunction with the accompanyname of a nickel based alloy comprising small amounts of molybdenum, iron and carbon. A thin insulating layer or film 33, such as A1 is vflame sprayed onto the inner surface of cylindrical mounting member 30. The insulating layer 33 has, preferably, a thickness of one mil and is concentric with the metallic mounting member 30.

The cathode 14 further comprises a base cup 34 which is formed by a cylindrical ceramic member 35 and a metal cap 36 brazed to a metallized surface on the inside of the ceramic member 35. A pin 37 extends through an aperture 38 in the metal cap 36. The pin 37 also extends through an aperture 39 in metal cap 40 which is brazed to a metallized surface on the inside of a ceramic cylinder section 41. The pin 37 is not fixed to caps 36 and 40 thuspermitting the pin 37 to slide through the apertures 38 and 39. A spring 42 is mounted below plate 43 which. is connected to the pin 37. A plate 44 is also connected to the pin 37 adjacent the cap 40.

Referring to FIGURES 2 and 3, the ceramic cylinder 35 has a plurality of longitudinal grooves 45 and lands 47 disposed about its circumference. Each land 47 is metallized 48 and a pair of parallel bars 49 are brazed onto each land 47. The bars 49 are preferably .001 inch thick and .035 inch wide and are made of Hastelloy B metal which is a trade name of a nickelbased alloy containing molybdenum, iron and carbon. The metallized portion 48 serves to electrically connect adjacent bars 49 mounted on each land 47. The grooves 45 serve to electrically insulate each pair of bars 49 from the otherpairs. Each one of a pair of filament tabs 51 are attached to a different one of the pairs of parallel bars 49. The filament tabs 51 are connected to the prongs 22 and 23 and thus serve as leads for applying a heating current to the bars 49 on which an electron emissive oxide coating is applied. The electron emissive coating is applied to substantially the entire portion of the metal bars 49 extending between ceramic cylinder 35 and ceramic cylinder section 41. A similar series of grooves and lands are formed on the ceramic cylinder section 41 with the lands being metallized to hold the pairs of bars 49 brazed thereto. The metallized lands also serve to electrically connect adjacent bars 49; It will be understood that the interconnection of the ends of adjacent bars 49 by the metallizing 43 forms in effect a continuous strip. Thus, a heating current applied to the bars 49 will cause them to heat up and they will be permitted to expand by means of the spring 42 acting against the plate 43, The bars 49 will be kept taut at all .times by the spring 42 cooperating with the plate 43 which is connected to the pin 37 which, in turn, slides through the metal cap 36.

FIGURES 4 and 5 show two dilferent arrangements of the metal bars 49 used in the cathode 14 of FIGURES l and 2. FIGURE 4 shows a series arrangement wherein all the metal bars 49 are electrically connected in'series by the metallizing portions 48 and each of the twofilament tabs 51 is connected to one of the parallel bars 49 to provide the series arrangement.

FIGURE 5 shows an arrangement of the metal bars 49 wherein the portion of the-bars 49 designated A are con nected in parallel to the remainder of the filament bars 49 designated by brackets B by means of the metallizing portions 48.

It can be appreciated that the above-described arrangements are merely illustrations of the-principles of the invention. Numerous other arrangements and modifications may be devised by one skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron tube having an envelope enclosing electrodes including a cathode, said cathode comprising a cylindrical metallic mounting memberfor carrying R.F. energy that is to be amplified, a thin insulating film on said cylindrical mounting member and concentric there with, a plurality of thin metal parallel bars mounted on the surface of said thin insulating film, said metal bars having a portion thereof capacitively coupled through the insulating layer to the cylindrical metallic mounting mem her to shorten the inductive path for the RP. energy to be amplified, said metal bars having an electron emissive portion which is not capacitively coupled to said'cylindrical metallic mounting member, a cylindrical ceramic member having a plurality of grooves and lands on the outer surface thereof, said lands having a metallized layer thereon, said portion of the metal bars capacitively coupled to the cylindrical mounting member being mounted on the metallized lands of said cylindrical ceramic memher, a cylindrical ceramic section have a plurality of grooves and lands on the outer surface thereof, said lands having a metallized layer thereon, one end of said metal bars being mounted on the metallized lands of said cylindrical ceramic section, the electron emissive portion of said metal bars being located between said cylindrical ceramic member and said cylindrical ceramic section, a first metal cap mounted within said cylindrical ceramic member, said first metal cap having an aperture therein, a second metal cap mounted within said cylindrical ceramic section, said second metal cap having an aperture therein, a pin extending through the apertures in said first and second metal caps, a first plate connected to said pin adjacent said first metal cap, a second plate connected to said pin adjacent said second metal cap and adapted to engage the inner surface of said second metal cap, a spring mounted between said first metal cap and said first metal plate, said first and second metal caps cooperating with said spring and said first and second metal plates to hold said metal bars taut between said cylindrical ceramic member and said cylindrical ceramic section.

2. A directly heated cathode assembly comprising means forming an electron emissive surface for emitting electrons from said cathode, said electron emissive means comprising an electron emissive strip forming a long path of high inductance to RF. current flow, and RF. by-pass means forming a common coupling to plural locations spaced along said long path for connecting R.F. current simultaneously to said spaced locations, whereby said long path is shortened as regards RF. current flow and remains long as regards substantially direct current flow, said R.F. by-pass means being coupled to said long path solely at said spaced locations, and said emissive strip having a substantial electron emissive part thereof which is intermediate said spaced by-pass locations.

3. A cathode-assembly as claimed in claim 2 in which said electron emissive strip is arranged in spaced lengths lying in a substantially cylindrical shape; each said length having one end connected to the adjacent length on one side and having the other end connected to the adjacent length on the other side, and said by-pass means comprises a metallic cylinder, and a thin dielectric cylinder forming a radial separation between said metallic cylinder and said cylindrically arranged strip.

4. An electron tube having an envelope enclosing electrodes including a directly heated cathode having an electron emissive surface, and another electrode directly adjacent said emissive surface, said cathode comprising a strip of metallic material forming a long path of high inductance to RF. current flow, and RF. by-pass means forming a common coupling to plural locations spaced along said long path for connecting RF. current simultaneously to said spaced locations, whereby said long path is shortened as regards R.F. current flow and remains long as regards direct current flow, said R.F. by-pass means being coupled to said long path solely at said spaced locations, and said strip having a substantial electron emissive area which is intermediate said spaced by-pass locations.

5. An electron tube as claimed in claim 4 in which said strip of metallic material is arranged in spaced lengths lying in a substantially cylindrical shape; each said length having one end connected to the adjacent length on one side and having the other end connected to the adjacent length on the other side, and said bypass means comprises a metallic cylinder, and a thin dielectric cylinder forming a radial separation between said metallic cylinder and said cylindrically arranged strip.

6. An electron tube as claimed in claim 5 further comprising a lead for said metallic cylinder extending to the outside of said envelope to form a terminal for RF. current supply to said metallic cylinder, and a lead for said metallic strip extending to the outside of said envelope to form a terminal for direct current supply to said strip.

7. An electron tube having an envelope enclosing electrodes including a cathode, said cathode comprising a cylindrical metallic mounting member for carrying R.F. energy that is to be amplified, a thin insulating film on said cylindrical mounting member and concentric therewith, a plurality of thin metal parallel bars mounted on the surface of said thin insulating film, said metal bars having a portion thereof capacitively coupled through the insulating layer to the cylindrical metallic mounting member to shorten the inductive path for the RF. energy to be amplified, a cylindrical ceramic member having a plurality of grooves and lands on the outer surface thereof, said lands having a metallized layer thereon, said portion of the metal bars capacitively coupled to the cylindrical mounting member being mounted on the metallized lands of said cylindrical ceramic member, a cylindrical ceramic section having a plurality of grooves and lands on the outer surface thereof, said lands having a metallized layer thereon, one end of said metal bars being mounted on the metallized lands of said cylindrical cer'amic section, and the portion of said metal bars located between said cylindrical ceramic member and said cylindrical ceramic section being electron emissive.

References Cited by the Examiner UNITED STATES PATENTS 2,057,931 10/1936 Stupakotf 313-342 X 2,385,435 9/1945 Werner et a1 313278 2,391,927 1/ 1946 Segerstrom 31563 2,416,298 2/1947 Fisk 31539.63 X 2,642,533 6/1953 Preist 315-39 X 2,681,997 6/1954 Haeff et a1 31539 X 2,693,552 11/1954 Steinberg 315337 2,932,759 4/1960 Shepherd 313-337 2,985,946 '5/1961 Deweijer et al. 313337 3,108,171 10/1963 Vary 313-341 X JAMES D. KALLAM, Primary Examiner. DAVID J. GALVIN, Examiner. A. I. JAMES, Assistant Examiner. 

1. AN ELECTRON TUB HAVING AN ENVELOPE ENCLOSING ELECTRODES INCLUDING A CATHODE, SAID CATHODE COMPRISING A CYLINDRICAL METALLIC MOUNTING MEMBER FOR CARRING R.F. ENERGY THAT IS TO BE AMPLIFIED, A THIN INSULATING FILM ON SAID CYLINDRICAL MOUNTING MEMBER AND CONCENTRIC THEREWITH, A PLURALITY OF THIN METAL PARALLEL BARS MOUNTED ON THE SURFACE OF SAID THIN INSULATING FILM, SAID METAL BARS HAVING A PORTION THEREOF CAPACITIVELY COUPLED THROUGH THE INSULATING LAYER OF THE CYLINDRICAL METALLIC MOUNTING MEMBER TO SHORTEN THE INDUCTIVE PATH FOR THE R.F. ENERGY TO BE AMPLIFIED, SAID METAL BARS HAVING AN ELECTRON EMISSIVE PORTION WHICH IS NOT CAPACITIVELY COUPLED TO SAID CYLINDRICAL METALLIC MOUNTING MEMBER, A CYLINDRICAL CERAMIC MEMBER HAVING A PLURALITY OF GROOVES AND LANDS ON THE OUTER SURFACE THEREOF, SAID LANDS HAVING A METALLIZED LAYER THEREON, SAID PORTION ON THE METAL BARS CAPACITIVELY COUPLED TO THE CYLINDRICAL MOUNTING MEMBER BEING MOUNTED ON THE METALLIZED LANDS OF SAID CYLINDRICAL CERAMIC MEMBER, A CYLINDRICAL CERAMIC SECTION HAVE A PLURALITY OF GROOVES AND LANDS ON THE OUTER SURFACE THEREOF, SAID LANDS HAVING A METALLIZED LAYER THEREON, ONE END OF SAID METAL BARS BEING MOUNTED ON THE METALLIZED LANDS OF SAID CYLINDRICAL CERAMIC SECTION, THE ELECTRON EMISSIVE PORTION OF 